Vertical type light emitting device having transparent electrode and method of manufacturing the same

ABSTRACT

Provided is a vertical type light emitting device and a method of manufacturing the same. A transparent electrode having high transmittance with respect to light in the entire range and constructed by using a resistance change material of which resistance state is to be changed from a high resistance state to a low resistance state if a voltage exceeding a threshold voltage inherent in a material is applied so that conducting filaments are formed is formed between an electrode pad and a semiconductor layer of a light emitting device. The transparent electrode has high transmittance with respect to the light in a UV wavelength range as well as in a visible wavelength range generated in the light emitting device. Since the conductivity of the transparent electrode is heightened due to the formation of the conducting filaments, the transparent electrode has good ohmic contact characteristic with respect to a semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device and a method ofmanufacturing the light emitting device, and more particularly to, alight emitting device including a transparent electrode and a method ofmanufacturing the light emitting device.

2. Description of the Related Art

Recently, in order to improve performance of a white-light LED used forvarious applications such as a backlight source of an LCD display,solid-state lighting (SSL), and flashlight, high efficiency/high powerGaN based LEDs have been actively researched.

However, in a lateral-conducting GaN-based LED having a simple structurewhich is widely used in the related art, since anode and cathode aredesigned to be formed in the same direction, a current concentrationeffect (current-crowding effect; CCE) occurs in the n-type electrode,and particularly, a thermal problem occurs due to insulating propertiesof sapphire used for a substrate. Therefore, the lateral-conductingGaN-based has a limitation in improving output power of the LED byinjecting high current.

In order to solve the above-mentioned problems of the lateral-conductingGaN-based LED, a vertical-conducting structure LED (VLED) whereelectrodes are designed to be formed above and below the LED has beenresearched. In addition, a vertical-conducting structure metal-substrateGaN LED (VM-LED) where a sapphire substrate is lifted off by using laser(laser lift-off; LLO) and a metal is used as a substrate for efficientlyreleasing heat has been researched.

In comparison to the lateral-conducting structure GaN-based LED, theperformance of the VM-LED is greatly improved. Namely, the output powerP₀ of the VM-LED is increased, and the operating voltage (forwardvoltage; V_(F)) thereof is decreased. However, in the manufacturing ofthe high-power LED, there are still the problems of currentconcentration (current crowding) in the portion below the n-type metalcontact pad into current is injected, non-uniform current dispersion,and non-uniform light emission.

In order to solve the problems, in many research groups, an N-face n-GaNlayer where a convex-concave pattern is formed and metal are formed tobe in good ohmic contact to implement uniform current injection anduniform current dispersion in the n-type electrode of the VLED. Inaddition, in many research groups, the n-type electrode is efficientlydesigned to implement uniform current dispersion and uniform currentinjection.

In order to implement uniform current dispersion and injection, thecontact area of the n-electrode is allowed to be increased (n-electrodepattern design), or a current blocking layer (CBL) is used. In addition,a transparent conduction layer (TCL) and a transparent conductionelectrode (TCE) may also be inserted between the n-electrode and the GaNlayer. However, the above-mentioned techniques in the related art havethe problems, as follows.

First, if the contact area of the n-type electrode is increased, uniformcurrent dispersion and injection can be advantageously implemented.However, since light emitted from an activation layer (multi quantumwell; MQW) is blocked or absorbed, light extraction efficiency isdeteriorated.

In the case where a current blocking layer is inserted, since thecurrent blocking layer is formed by inserting an insulating materialhaving almost the same size as the n-type electrode into a symmetricposition of the p-GaN layer, current concentrated below the n-typeelectrode can be advantageously dispersed. However, since current doesnot flow through the current blocking layer, the current can be injectedinto the portion excluding the current blocking layer. Namely, since thecurrent is not injected through the entire area of the p-GaN layer,there is a problem in terms of efficiency. In addition, since thecurrent blocking layer needs to be formed at an accurate position withan accurate size, there is difficulty in the manufacturing process.

Finally, in the technique of inserting a transparent conduction layer,there is an advantage in that current can be effectively dispersed andinjected by using an n-type electrode having a small area. However, whenthe light is emitted out, since the light is absorbed by the transparentconduction layer, for example, ITO (indium tin oxide), IZO (indium zincoxide), there is a problem in that the light extraction efficiency isdecreased.

In the case of the UV-LED for which demands have been greatly increasedrecently, the problem of decrease in light extraction efficiency becomesmore serious.

FIG. 1 is a graph illustrating transmittance in the case where an ITOtransparent electrode is formed on a p-GaN semiconductor layer in therelated art. As illustrated in FIG. 1, the transmittance of the ITOtransparent electrode is 80% or more in a wavelength range of 350 nm ormore, but the transmittance is greatly decreased in a short wavelengthrange, that is, a UV wavelength range. Particularly, in a shortwavelength range of 280 nm or less, the transmittance is decreased downto 20% or less. In order to solve the problem, in another technique inthe related art, the transparent electrode is not formed on thesemiconductor layer such as a p-AlGaN layer, but a metal electrode padis directly formed thereon. However, since a different in work functionbetween the metal and the semiconductor layer is too large, ohmiccontact is not formed therebetween, and current is concentrated on themetal electrode pad so as not to spread over the entire activationlayer. In other words, the above-described problems still occur.

Although various researches have been made in order to solve theabove-described problems, a transparent electrode capable of solving theproblem of current concentration and implementing high transmittance andhigh conductivity with respect to light in a UV wavelength range has notbeen developed. This is because conductivity and transmittance of amaterial has a trade-off relationship. Since a material having as hightransmittance as it can be used in a UV wavelength range has a largeband gap (larger than the band gap (3.4 eV) of ITO), the material hastoo low conductivity to be used as an electrode and is not in ohmiccontact with a semiconductor material. Therefore, it is impossible touse the material as an electrode.

SUMMARY OF THE INVENTION

The present invention is to provide a vertical type light emittingdevice including a transparent electrode having high transmittance andgood ohmic contact characteristic with respect to a semiconductor layerand capable of solving a problem of current concentration with respectto light in the entire wavelength range including visible light and UVlight and a method manufacturing the vertical type light emittingdevice.

According to an aspect of the present invention, there is provided avertical type light emitting device including: a substrate; a reflectivelayer which is formed on the substrate; a second semiconductor layerwhich is formed on the reflective layer; an activation layer which isformed on second semiconductor layer to generate light; a firstsemiconductor layer which is formed on the activation layer; and atransparent electrode which is formed on first semiconductor layer byusing a transparent insulating material of which resistance state is tobe changed from a high resistance state into a low resistance stateaccording to an applied electric field.

In the above aspect, a forming process may be performed on thetransparent electrode by applying a threshold voltage or more inherentin a material of the transparent electrode, so that conducting filamentsare formed in the transparent electrode.

In addition, in the above aspect, a convex-concave pattern may be formedon a surface of the transparent electrode.

In addition, in the above aspect, the transparent electrode may beconfigured to include a plurality of transparent electrode layers ofwhich refractive indexes are gradually decreased.

In addition, in the above aspect, the transparent electrode may beformed with any one of a transparent oxide based material, a transparentnitride based material, a transparent polymer based material, and atransparent nano material.

In addition, in the above aspect, the vertical type light emittingdevice may further include a current spreading layer which is formed byusing CNT (carbon nano tube) or graphene between the first semiconductorlayer and the transparent electrode.

In addition, in the above aspect, the vertical type light emittingdevice may further include a current spreading layer which is formed byusing CNT or graphene and is in contact with a surface of transparentelectrode opposite to a surface of the transparent electrode which is incontact with the first semiconductor layer.

In addition, in the above aspect, the first semiconductor layer may beformed with an n-AlGaN layer or an n-GaN layer, and the secondsemiconductor layer may be formed with a p-AlGaN layer or a p-GaN layer.

According to another aspect of the present invention, there is provideda method of manufacturing a vertical type light emitting device,including: (a) forming a transparent electrode on a substrate by using atransparent insulating material of which resistance state is to bechanged from a high resistance state into a low resistance stateaccording to an applied electric field; (b) sequentially forming a firstsemiconductor layer, an activation layer which generates light, a secondsemiconductor layer, and a reflective layer on the transparentelectrode; (c) bonding a submount substrate so as to be in contact withthe reflective layer and separating the substrate; and (d) changing theresistance state of the transparent electrode into a low resistancestate by applying a voltage to the transparent electrode.

In the above aspect, the (d) changing of the resistance state may beperforming a forming process by applying a threshold voltage or more tothe transparent electrode, so that conducting filaments are formed inthe transparent electrode.

In addition, in the above aspect, the (c) bonding of the submountsubstrate may further include: (c1) forming a bonding layer on thereflective layer and bonding a submount substrate to the bonding layer;and (c2) separating the substrate from the transparent electrode.

In addition, in the above aspect, the (d) changing of the resistancestate may be forming a convex-concave pattern on a surface of thetransparent electrode and changing a resistance state of the transparentelectrode into a low resistance state.

In addition, in the above aspect, in the (a) forming of the transparentelectrode, the transparent electrode may be configured by sequentiallyforming a plurality of transparent electrode layers of which refractiveindexes are gradually increased.

In addition, in the above aspect, the transparent electrode may beformed by using any one of a transparent oxide based material, atransparent nitride based material, a transparent polymer basedmaterial, and a transparent nano material.

In addition, in the above aspect, the method may further include,between the (a) forming of the transparent electrode and the (b)sequentially forming of the first semiconductor layer, the activationlayer which generates light, the second semiconductor layer, and thereflective layer, forming a current spreading layer on the transparentelectrode by using CNT or graphene, wherein, in the (b) sequentiallyforming of the first semiconductor layer, the activation layer whichgenerates light, the second semiconductor layer, and the reflectivelayer, the first semiconductor layer is formed on the current spreadinglayer.

In addition, in the above aspect, the method may further include forminga current spreading layer on the transparent electrode of whichresistance state is changed into a low resistance state by using CNT orgraphene.

In addition, in the above aspect, the first semiconductor layer may beformed with an n-AlGaN layer or an n-GaN layer, and the secondsemiconductor layer may be formed with a p-AlGaN layer or a p-GaN layer.

In the present invention, a transparent electrode having hightransmittance with respect to light in the entire range and constructedby using a resistance change material of which resistance state is to bechanged from a high resistance state to a low resistance state if avoltage exceeding a threshold voltage inherent in a material is appliedso that conducting filaments are formed is formed between a electrodepad and a semiconductor layer of a light emitting device.

Therefore, according to the present invention, current injected into anelectrode pad is allowed to spread from the transparent electrode overthe entire area of the light emitting device, so that the problem ofcurrent concentration is solved. The transparent electrode has hightransmittance with respect to the light in a UV wavelength range(particularly, the light in a UV wavelength range of 340 nm to 280 nmand the light in a UV wavelength range of 280 nm or less) as well as thelight in a visible wavelength range generated in the light emittingdevice. Since the conductivity of the transparent electrode isheightened due to the formation of the conducting filaments, thetransparent electrode has good ohmic contact characteristic with respectto a semiconductor layer.

In addition, in the present invention, in the case where a currentspreading layer formed by using CNT or graphene having good conductivityand transmittance characteristics is further formed on the upper orlower portion of the transparent electrode, conducting filaments formedin the transparent electrode are allowed to be connected to each other,so that the current flowing into the transparent electrode is allowed tospread over the semiconductor layer. Therefore, the currentconcentration phenomenon can be effectively prevented.

In addition, in the present invention, the transparent electrode ofwhich refractive index (1.5 to 2.4) is smaller than that of asemiconductor layer is formed between air (refractive index=1) and thesemiconductor layer (n-type GaN; refractive index=2.46), so that totalreflection can be reduced due to a large difference in refractive indexat the interface. Therefore, the light extraction efficiency can befurther improved.

In addition, in the present invention, instead of ITO or IZO transparentelectrodes in the related art which requires thermal treatment forimproving optical characteristics, the transparent electrode in whichthe conducting filaments are to be formed to implement excellent opticalcharacteristics without thermal treatment is used. Therefore, it ispossible to improve electric characteristics and optical characteristicsof the light emitting device in comparison to the light emitting devicein the related art.

In addition, in the present invention, a convex-concave pattern isformed on a surface of the transparent electrode, or the transparentelectrode is formed in a multi-layered structure, so that the refractiveindex can be adjusted. Therefore, it is possible to further improveoptical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a graph illustrating transmittance in the case where an ITOtransparent electrode is formed on a p-GaN semiconductor layer in therelated art;

FIG. 2 is a diagram illustrating a configuration of a vertical typelight emitting device including a transparent electrode according to afirst embodiment of the present invention;

FIGS. 3 a and 3 b are diagrams illustrating characteristics of aresistance change material;

FIG. 4 is a diagram illustrating processes of manufacturing a verticaltype light emitting device where the transparent electrode is formedaccording to the first embodiment of the present invention;

FIGS. 5 a and 5 b are diagrams illustrating a configuration of avertical type light emitting device according to a second embodiment ofthe present invention;

FIG. 6 is a graph illustrating transmittance-wavelength curves of an ITOtransparent electrode and a transparent electrode (Si₃N₄) according tothe embodiment of the present invention;

FIG. 7 a is a graph illustrating operating voltage characteristics ofthe light emitting device according to the embodiment of the presentinvention; and

FIG. 7 b is a graph illustrating output characteristics of the lightemitting device according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the attached drawings.

FIG. 2 is a diagram illustrating a configuration of a vertical typelight emitting device including a transparent electrode according to afirst embodiment of the present invention.

Referring to FIG. 2, the vertical type light emitting device accordingto the first embodiment of the present invention is configured bysequentially forming a reflective layer 170, a second semiconductorlayer 160, an activation layer 150, a first semiconductor layer 140, anda transparent electrode 130 on a substrate 200 and by forming an n-typeelectrode pad 190 on the transparent electrode 130.

The substrate 200 may be configured by using a substrate which isgenerally used for manufacturing a vertical type light emitting device.P-type ohmic metal may be formed on each of two surfaces of thesubstrate 200. In addition, a reflective layer 170 is formed on thesubstrate 200. The reflective layer 170 may be formed by using Ag, Al,Pt, Au, Ni Ti, ITO, or a combination thereof. Namely, there is nolimitation to the material of the reflective layer.

The second semiconductor layer 160 is a semiconductor layer doped as a ptype. In the embodiment of the present invention, the secondsemiconductor layer 160 is formed with a single layer of p-GaN. Inaddition, the second semiconductor layer 160 is formed with a singlelayer of p-AlGaN so as to generate light in a UV wavelength range, orthe second semiconductor layer 160 is formed by sequentially forming ap-GaN layer and a p-AlGaN layer. However, the second semiconductor layermay also be formed with a general material used for manufacturing alight emitting device.

In the embodiment of the present invention, it is preferable that theactivation layer 150 (MQW) is formed with Al(In)GaN/(In)GaN so as togenerate light in a UV wavelength range. However, any material capableof generating light in a UV wavelength range can be used for theactivation layer 150 of the light emitting device without limitation.

The first semiconductor layer 140 is a semiconductor layer doped as an ntype. In the embodiment of the present invention, the firstsemiconductor layer 140 is formed with n-GaN, or the first semiconductorlayer 140 is formed with n-AlGaN so as to generate light in a UVwavelength range. However, the first semiconductor layer may also beformed with a general material used for manufacturing a light emittingdevice.

In the above-described embodiment, the first semiconductor layer 140 andthe second semiconductor layer 160 are semiconductor layers doped as ann type and a p type, respectively. The reverse case is also available.

The transparent electrode 130 formed on the first semiconductor layer140 according to the embodiment of the present invention is constructedwith a transparent material (resistance change material) which has hightransmittance with respect to light in a UV wavelength range and ofwhich resistance state is to be changed according to an applied electricfield. The resistance change material is mainly used in the field ofReRAM (resistive RAM). If a threshold voltage or more inherent in thematerial is applied to the material, electrical break-down phenomenonoccurs and electro-forming is performed, so that the resistance state ofthe resistance change material which is originally an insulatingmaterial is changed from a high resistance state into a low resistancestate. Therefore, the material has conductivity.

More specifically, if a threshold voltage or more is applied to theresistance change material which is an insulating material, electrodemetal materials are inserted into a thin film due to electric stress(forming process), or a defective structure occurs in the thin film, sothat conducting filaments 132 (or, metallic filaments) are formed in theresistance change material as illustrated in FIG. 2. After that,although the voltage applied to the material is removed, the conductingfilaments 132 remain, and current can flow through the conductingfilaments 132, so that the low resistance state of the material ismaintained.

Referring to FIG. 3 a, it can be seen that the resistance changematerial (for example, AlN) has an insulating characteristic before theforming process and has an I-V characteristic of a metal after theforming process.

FIG. 3 b is a graph illustrating how long the resistance state can bestably maintained after the conducting filaments 132 are formed. It canbe seen from a dotted line in the graph that the low resistance statecan be stably maintained for ten years after the conducting filaments132 are formed.

In the embodiment of the present invention, a transparent conductiveoxide based material (SiO₂, Ga₂O₃, Al₂O₃, ZnO, ITO, or the like), atransparent conductive nitride based material (Si₃N₄, AlN, GaN, InN, orthe like), a transparent conductive polymer based material (polyaniline(PANI)), poly (ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS)or the like), and a transparent conductive nano material (CNT,CNT-oxide, Graphene, Graphene-oxide, or the like) or the like may beused as the resistance change material. In addition to theabove-described materials, any material which is transparent and has theabove-described resistance change characteristic can be used to form thetransparent electrode 130 according to the present invention. It shouldbe noted that the statement that the material has conductivity denotesthat the material is allowed to have conductivity as a result of theforming process according to the electro break-down phenomenon, by whichthe conducting filaments 132 are formed in the transparent electrode. Inaddition, it should be noted that the forming process is performed onthe transparent electrode 130 according to the present invention, sothat the conducting filaments are formed in the transparent electrode.

In addition, generally, thermal treatment is performed in asemiconductor process. Due to the thermal treatment, electriccharacteristics of elements are deteriorated. In the present invention,it it found that, in the case where the electro-forming is performed dueto electrical break-down phenomenon in the transparent electrode, theelectric characteristics of the elements which are deteriorated due tothe thermal treatment can be recovered.

In addition, a convex-concave pattern is formed on the surface of theabove-described transparent electrode 130, so that light efficiency canbe further improved. In addition, the above-described transparentelectrode 130 may be configured with a plurality of layers so that therefractive indexes of the layers are gradually increased in thedirection toward the n-type electron pad 190. Therefore, totalreflection can be reduced due to a difference in refractive index, sothat light efficiency can be further improved.

On the other hand, as illustrated in FIG. 2, if the light emittingdevice is completed, the current injected through the n-type electrodepad 190 formed on the transparent electrode 130 spreads over the entirearea through the conducting filaments 132, which are connected to eachother in the transparent electrode 130, to be injected into the entirefirst semiconductor layer 140. The light in a UV wavelength range aswell as the light in a visible wavelength range generated in theactivation layer 150 is emitted out through the transparent electrodehaving a large band gap.

FIG. 4 is a diagram illustrating processes of manufacturing a verticaltype light emitting device where the transparent electrode is formedaccording to the first embodiment of the present invention.

The processes of manufacturing the vertical type semiconductor lightemitting device according to the first embodiment of the presentinvention will be described with reference to FIG. 4.

First, referring to (a) of FIG. 4, a buffer layer 120 is formed on asubstrate 110 such as a sapphire substrate, and a transparent electrode130 is formed on the buffer layer 120 by using a resistance changematerial. The buffer layer 120 may be formed by using GaN, AlN, or thelike. In addition, the material used for the transparent electrode isdescribed above. The method of fabricating the transparent electrode 130is the same as the method of fabricating a transparent electrode of ageneral light emitting device.

In addition, the above-described transparent electrode 130 may beconfigured with a plurality of layers so that the refractive indexes ofthe layers are gradually increased in the upward direction (in thedirection toward the first semiconductor layer 140). Therefore, in alight emitting device including the above transparent electrode, totalreflection can be reduced due to a difference in refractive index, sothat light efficiency can be further improved.

Next, an n-type first semiconductor layer 140 (for example, n-GaN,n-AlGaN, or the like) is formed on the transparent electrode 130. Afteran activation layer (MQW) 150 is formed on the first semiconductor layer140, a p-type second semiconductor layer 160 (for example, p-GaN,p-AlGaN, or the like) is formed on the activation layer 150. Next, areflective layer 170 is formed on the second semiconductor layer 160.The reflective layer 170 may be formed by using Al, Au, Ag, or othermaterials used for forming a reflective layer in the process ofmanufacturing a general LED.

Next, as illustrated in (b) of FIG. 4, a bonding layer (bonding metal)180 for bonding the submount substrate 200 is formed on the reflectivelayer 170. Next, the bonding layer 180 formed on the reflective layer170 is bonded to the submount substrate 200 so that the sapphiresubstrate 110 is disposed at the upper side. In order to separate thesapphire substrate 110 from the light emitting device, a UV laser beamhaving a wavelength range of 245 nm to 305 nm is irradiated through thesapphire substrate 110.

The irradiated laser beam passes through the sapphire substrate 110 andis absorbed at the interface between the sapphire substrate 110 and thebuffer layer 120, so that the buffer layer 120 and the substrate 110 areseparated from each other. In the case where the buffer layer 120 isformed by using GaN, the GaN of the buffer layer 120 absorbing the UVlaser beam is decomposed into Ga and N₂. The generated N₂ is released toan external portion, so that only Ga remains on the interface. The Gahaving a melting point of about 30° C. is melted by applied heat, sothat the sapphire substrate 110 is separated.

Next, as illustrated in (c) of FIG. 4, after the substrate 110 isseparated, the remaining buffer layer 120 is removed through an etchingprocess so that the transparent electrode 130 is exposed. A photoresistlayer (not shown) is formed on the exposed transparent electrode 130,and a pattern for forming the forming electrode 410 is formed on aportion of the area of the photoresist layer where an n-type metal pad190 is to be formed by performing a photolithography process. Next, byperforming an e-beam process, a sputtering process, or other metaldeposition processes, the forming electrode 410 is formed in thepattern. Next, the forming electrode 410 is completed by removing thephotoresist layer except for the forming electrode 410 through alift-off process.

Next, as illustrated in (d) of FIG. 4, if a a threshold voltage or moreinherent in the material is applied to the forming electrode 410 formedon the transparent electrode 130, the forming process caused by theelectrical break-down is performed, so that the conducting filaments 132are formed in the transparent electrode 130 which is an insulatingmaterial. Accordingly, the resistance state of the transparent electrode130 is changed from a high resistance state into a low resistance state.

In this case, before the forming process is performed, a convex-concavepattern may be additionally formed on the surface of the transparentelectrode 130, so that the light efficiency can be further improved. Themethod of forming the convex-concave pattern on the transparentelectrode 130 may employ a well-known method in the related art, andthus, the detailed description thereof is omitted.

After the conducting filaments 132 are formed in the transparentelectrode 130, as illustrated in (e) of FIG. 4, an n-type metalelectrode pad 190 is formed on the transparent electrode 130. At thistime, as a method of forming the metal electrode pad 190, the formingelectrode 410 for performing the forming process may be removed, and aseparate metal electrode pad may be formed. Alternatively, metal isadditionally deposited on the forming electrode 410 by using a mask (notshown), so that the n-type metal electrode pad 190 may be formed.

Hereinbefore, the light emitting device according to the firstembodiment of the present invention and the method of manufacturing thelight emitting device are described.

In the first embodiment described above with reference to FIGS. 2 to 4,some conducting filaments 132 formed in the transparent electrode 130may not be connected to other conducting filaments 132. In this case,current flowing into the transparent electrode 130 may not spread overthe entire transparent electrode 130 but be concentrated to belocalized, so that a problem of current concentration that current isconcentrated to be localized on the first semiconductor layer 140 whichis in contact with the transparent electrode 130 may occur.

FIGS. 5 a and 5 b are diagrams illustrating configurations of lightemitting devices according to the second embodiment of the presentinvention for solving the problem of current concentration.

In the examples illustrated in FIGS. 5 a and 5 b, in order to improvethe current spreading characteristics of the transparent electrode 130,a current spreading layers 134 or 136 formed by using CNT (carbon nanotube) or graphene which connects the conducting filaments 132 formed inthe transparent electrode 130 is formed on an upper or lower surface ofthe transparent electrode 130.

FIG. 5 a illustrates an example where the current spreading layer 134formed by using CNT or graphene is formed between the transparentelectrode 130 and the second semiconductor layer 160. FIG. 5 billustrates an example where the current spreading layer 136 formed byusing CNT or graphene is formed on the transparent electrode 130.

The CNT and graphene have good conductivity and transmittancecharacteristics. In the present invention, the conducting filaments 132in the transparent electrode 130 are connected to each other by formingthe current spreading layers 134 and 136 by using CNT or graphene on onesurface of the transparent electrode 130 by using the characteristics,so that the current flowing into the transparent electrode 130 can beallowed to spread over the entire first semiconductor layer 140.

At this time, as the thickness of the current spreading layers 134 and136 is increased, CNTs and graphenes are connected to each other, andthus, the possibility that the conducting filaments 132 are connected toeach other is increased. As a result, the conductivity of thetransparent electrode 130 is increased, but the transmittance thereof isdecreased. Therefore, it is preferable that the current spreading layers134 and 136 according to the present invention are formed with athickness enough to connect the conducting filaments 132 in thetransparent electrode 130 to each other and as thin as possible within arange where the transmittance is not deteriorated.

In the second embodiment of the present invent illustrated in FIGS. 5 aand 5 b, the current spreading layers 134 and 136 are formed with athickness of about 2 nm to about 100 nm. The thickness of 2 nm is aminimum thickness so that a single layer of CNT or graphene can beformed, and the thickness of 100 nm is a maximum thickness so thattransmittance can be maintained to be 80% or more.

The manufacturing processes of the example illustrated in FIG. 5 a arethe same as those of the example described with reference to FIG. 4,except that the current spreading layer 134 is formed by using CNT orgraphene just after the transparent electrode is formed and the firstsemiconductor layer 140 is formed on the current spreading layer 134,and thus, the detailed description thereof is omitted.

The manufacturing processes of the example illustrated in FIG. 5 b arethe same as those of the example described with reference to FIG. 4,except that the current spreading layer 136 is formed by using CNT orgraphene just after the conducting filaments 132 are formed in thetransparent electrode 130 by performing the forming process and then-type electrode pad 190 is formed on the current spreading layer 136,and thus, the detailed description thereof is omitted.

FIG. 6 is a graph illustrating transmittance of an ITO transparentelectrode in the related art and transmittance of the transparentelectrode (Si₃N₄) according to the embodiment of the present inventionin wavelength ranges.

The ITO transparent electrode and the transparent electrode (Si₃N₄) areformed with the same thickness of 20 nm. Referring to FIG. 6, it can beunderstood from the result of comparison of the transmittance of the ITOtransparent electrode in the related art and the transmittance of thetransparent electrode (Si₃N₄) in which the conducting filaments areformed according to the embodiment of the present invention inwavelength ranges that the transparent electrode (Si₃N₄) according tothe present invention has high transmittance in the entire wavelengthranges. Particularly, it can be understood that the transparentelectrode (Si₃N₄) according to the present invention has very hightransmittance in the short wavelength range in comparison to the ITOtransparent electrode in the related art.

FIG. 7 a is a graph illustrating operating voltage characteristics ofthe light emitting device according to the embodiment of the presentinvention, and FIG. 7 b is a graph illustrating output characteristicsof the light emitting device according to the embodiment of the presentinvention.

Referring to FIGS. 7 a and 7 b, a general vertical type light emittingdevice in the related art in which no transparent electrode is insertedis selected as a reference light emitting device, and characteristics ofa vertical type light emitting device where an ITO transparent electrodehaving a thickness of 20 nm is formed as a current dispersion layer andcharacteristics of a vertical type light emitting device where thetransparent electrode (Si₃N₄) having a thickness of 20 nm according tothe embodiment of the present invention is formed as a currentdispersion layer are compared.

In terms of the operating voltage V_(F), it can be understood that theperformance of the light emitting devices where the current dispersionlayer is improved in comparison to the reference light emitting device.In addition, it can be understood that the performance of the lightemitting device where the transparent electrode (Si₃N₄) is formedaccording to the embodiment of the present invention is further improvedin comparison to the light emitting device where the ITO transparentelectrode is formed.

In terms of the output power P₀, it can be understood that theperformance of the light emitting devices according to the embodiment ofthe present invention is improved in comparison to the reference lightemitting device. However, it can be understood that the performance ofthe light emitting device where the ITO transparent electrode is formedis deteriorated in comparison to the reference light emitting device.

Accordingly, it can be understood that a vertical type light emittingdevice where the transparent electrode according to the presentinvention (Si₃N₄) in which the conducting filaments are formed due tothe electrical break-down phenomenon is formed has excellentperformances in terms of current dispersion effect, transmittance, andother electric characteristics.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

What is claimed is:
 1. A vertical type light emitting device comprising:a substrate; a reflective layer which is formed on the substrate; asecond semiconductor layer which is formed on the reflective layer; anactivation layer which is formed on second semiconductor layer togenerate light; a first semiconductor layer which is formed on theactivation layer; and a transparent electrode which is formed on firstsemiconductor layer by using a transparent insulating material of whichresistance state is to be changed from a high resistance state into alow resistance state according to an applied electric field.
 2. Thevertical type light emitting device according to claim 1, wherein aforming process is performed on the transparent electrode by applying athreshold voltage or more inherent in a material of the transparentelectrode, so that conducting filaments are formed in the transparentelectrode.
 3. The vertical type light emitting device according to claim1, wherein a convex-concave pattern is formed on a surface of thetransparent electrode.
 4. The vertical type light emitting deviceaccording to claim 1, wherein the transparent electrode is configured toinclude a plurality of transparent electrode layers of which refractiveindexes are gradually decreased.
 5. The vertical type light emittingdevice according to claim 1, wherein the transparent electrode is formedwith any one of a transparent oxide based material, a transparentnitride based material, a transparent polymer based material, and atransparent nano material.
 6. The vertical type light emitting deviceaccording to claim 1, further comprising a current spreading layer whichis formed by using CNT (carbon nano tube) or graphene between the firstsemiconductor layer and the transparent electrode.
 7. The vertical typelight emitting device according to claim 1, further comprising a currentspreading layer which is formed by using CNT or graphene and is incontact with a surface of transparent electrode opposite to a surface ofthe transparent electrode which is in contact with the firstsemiconductor layer.
 8. The vertical type light emitting deviceaccording to claim 1, wherein the first semiconductor layer is formedwith an n-AlGaN layer or an n-GaN layer, and the second semiconductorlayer is formed with a p-AlGaN layer or a p-GaN layer.
 9. A method ofmanufacturing a vertical type light emitting device, comprising: (a)forming a transparent electrode on a substrate by using a transparentinsulating material of which resistance state is to be changed from ahigh resistance state into a low resistance state according to anapplied electric field; (b) sequentially forming a first semiconductorlayer, an activation layer which generates light, a second semiconductorlayer, and a reflective layer on the transparent electrode; (c) bondinga submount substrate so as to be in contact with the reflective layerand separating the substrate; and (d) changing the resistance state ofthe transparent electrode into a low resistance state by applying avoltage to the transparent electrode.
 10. The method according to claim9, wherein the (d) changing of the resistance state is performing aforming process by applying a threshold voltage or more to thetransparent electrode, so that conducting filaments are formed in thetransparent electrode.
 11. The method according to claim 9, wherein the(c) bonding of the submount substrate further includes: (c1) forming abonding layer on the reflective layer and bonding a submount substrateto the bonding layer; and (c2) separating the substrate from thetransparent electrode.
 12. The method according to claim 9, wherein the(d) changing of the resistance state is forming a convex-concave patternon a surface of the transparent electrode and changing a resistancestate of the transparent electrode into a low resistance state.
 13. Themethod according to claim 9, wherein, in the (a) forming of thetransparent electrode, the transparent electrode is configured bysequentially forming a plurality of transparent electrode layers ofwhich refractive indexes are gradually increased.
 14. The methodaccording to claim 9, wherein the transparent electrode is formed byusing any one of a transparent oxide based material, a transparentnitride based material, a transparent polymer based material, and atransparent nano material.
 15. The method according to claim 9, furthercomprising, between the (a) forming of the transparent electrode and the(b) sequentially forming of the first semiconductor layer, theactivation layer which generates light, the second semiconductor layer,and the reflective layer, forming a current spreading layer on thetransparent electrode by using CNT or graphene, wherein, in the (b)sequentially forming of the first semiconductor layer, the activationlayer which generates light, the second semiconductor layer, and thereflective layer, the first semiconductor layer is formed on the currentspreading layer.
 16. The method according to claim 9, further comprisingforming a current spreading layer on the transparent electrode of whichresistance state is changed into a low resistance state by using CNT orgraphene.
 17. The method according to claim 9, wherein the firstsemiconductor layer is formed with an n-AlGaN layer or an n-GaN layer,and the second semiconductor layer is formed with a p-AlGaN layer or ap-GaN layer.